November 2024 Volume 6

EQUIPMENT & TECHNOLOGY

Production of Helical Gears by Axial Forming A feasibility study was initiated based on the presented state of the art and the consider ation of the significant advantages of axial forming over other helical gear manufac turing processes. The primary objective was to confirm the applicability of axial forming for manufacturing external helical gears. In cooperation with various partners, including Hofer powertrain GmbH, two components with different gear parameters were identi fied (Table 1). This experimental trial was

Figure 1: a) Principle of axial forming, b) force curve of the axial forming process with frequency modulation

Figure 1b shows the typical force curve of an incremental axial forming process. During the forward stroke, a forming process with a positive force or pressure component of the forming force occurs. Within the backward stroke, when the die is removed from the forming zone, only the frictional forces between the die and the component exist, which cause the negative components of the force curve. As part of a feasibility study, alternative forming manufacturing processes for the production of external helical gears were first considered so that the technological disadvantages of these processes against axial forming could finally be identified. The results of this literature review showed that axial forming combines the advan tages of the impact extrusion and rolling processes compared to the conventional metal forming manufacturing processes. Through the application of axial forming with frequency modulation as an incremental process, high contact stresses and high tool wear can be avoided. The main competitor to axial forming is the hobbing process. Axial forming can be considered as a new forming alterna tive to gear hobbing, which completely avoids material waste due to the full utilization of material and, thus, reduces material costs and the CO2 footprint. Moreover, forming in a one-piece tool results in an excellent total cumulative pitch deviation so that gear qualities of IT5-6 can be achieved compared to IT7 by hobbing. Furthermore, the axial forming process enables a compact design of the toothing because a distance of only 1.5-2 mm after the gear to the next shaft shoulder is necessitated. The long run-outs after the gear teeth, which are a technological requirement in gear hobbing, are therefore no longer necessary within axial forming [3 through 8]. Summarized, the analysis of state of the art showed that the described forming and machining processes are generally only suitable for external gearing. The production of internal helical gears is mainly realized by further machining processes, such as broaching, skiving, or flow-forming. However, these processes can only be applied to through holes and don’t offer any application possibility for gears in blind holes. The axial forming also, in this case, offers an economical alternative to machining and additionally provides the possibility for the manufacturing of internal helical gears in blind holes. A detailed analysis of the state of the art can be found in [9].

carried out according to [9] on an existing Felss Aximus H02 axial forming machine which was retrofitted with a driven tool carrier with a worm gear unit and servomotor. Thereby, a standard frequency modulation and a standard oil for highly loaded forming processes were applied for the forming of the helical gear components. The tolerances achieved in the trial (Figure 3a) demonstrate that forming an external gear through axial forming with a helix angle of 22° using the driven tool carrier is feasible. Moreover, similar quality ratios were determined for all gear components independent of gear heights and helix angles.

Table 1: Experimentally investigated helical geared components The gear component tolerances specified by the customer were achieved with the exception of the total helix deviation F β , and thus, axial forming was verified as a forming alternative to hobbing. The tolerance of total helix deviations F β of the helical gear compo nents produced on the Aximus H02 by axial forming showed a very specific trend over the length of the gearing which correlates with the occurrent varying load in the gearing die during forming. This observation indicates that there is a relationship between the finished part quality of the gear component and the occurrent different load dependent machine torsion. The forming of the gearing can be divided into three different load areas or forming areas on the component (cf. Figure 3a, red lines). The start of gear forming represents the first area where the required axial and torsional forces increase continuously to their maximum until the die-filling of the gear is reached. The subsequent main forming area extends over almost the entire length of the gear and

FIA MAGAZINE | NOVEMBER 2024 11